Conventional elevator installations have safety circuits consisting of safety elements connected in series. These safety elements monitor, for example, the status of shaft or car doors. Such a safety element can be a contact. An open contact shows that, for example, a door is open and a potentially impermissible door state has occurred. If, now, with the contact opened an impermissible open state of the door is identified then the safety circuit is interrupted. This has the consequence that a drive or brakes, which acts or act on the travel of an elevator car, brings the elevator car to a standstill.
A safety system for an elevator installation is known from the PCT patent specification WO2005/000727, which comprises a control unit as well as at least one bus junction and bus. The bus enables communication between the bus junctions and the control unit. The bus junction monitors, for example, the state of shaft and car doors by means of a safety element, which is a component of the bus junction. Moreover, the bus junction consists of a receiver and a transmitter. In that case the receiver is so designed that it reads digital default signals from the control unit, converts these into an analog signal and thus acts on the safety element. The transmitter in turn measures, after the safety element, the analog signal and converts this into a digital signal. The transmitter makes these digital data available to the control unit. These data are either sent by the bus junctions as digital signals to the control unit or demanded by the control unit by means of interrogation.
In order that safe operation of the elevator installation is guaranteed and the current state of the elevator installation known digital data has to be exchanged between the control unit and the bus junction at short time intervals. This means that the control unit has to have high computing capacities in order to be able to evaluate a multiplicity of digital signals and items of information. In addition, the bus is strongly loaded by signals, which are transmitted between the control unit and the bus junctions, and accordingly has high data transmission capacities.
An object of the present invention is thus to provide a monitoring method for an elevator installation with a reduced data exchange between control unit and bus junction and with a control unit having lower computing capacities.
The object is fulfilled by the invention in accordance with the definition of the independent claim.